Death row inmates in two states are taking legal action to stop states from using the kind of multi-drug protocol that resulted in botched executions in Oklahoma and Ohio.

The inmates are not challenging their convictions or death sentences, only the way in which the sentences are to be carried out, notes the Guardian.

Twenty-one death row inmates in Oklahoma filed suit against state officials, arguing the three-drug method used in that state violates the Constitution and amount to human experimentation, risking "severe pain, needless suffering and a lingering death," reports The New York Times.

In Arizona, six death row inmates filed a lawsuit against state officials alleging the state's two-drug combination also amounts to human experimentation.

The lawsuits follow Oklahoma's on April 29 execution of Clayton Lockett, who died of a heart attack 43 minutes after his execution began. As The Two-Way wrote in April, reporters witnessing the event said he writhed in apparent pain and tried to speak before officials drew a curtain, shielding him from view. Lockett had been convicted of shooting a 19-year-old and having her buried alive.

States are using new combinations of drugs because drugmakers, citing political and physical threats, have stopped producing traditional execution drugs such as sodium thiopental and pentobarbital. Oklahoma used the anesthetic midazolam, but would not disclose the source of the drugs and changed the procedure three times in the two months before the botched execution.

In Ohio, a new drug combination was administered to Dennis McGuire on January 16, the first execution there since the state ran out of pentobarbital. The Two-Way reported that McGuire gasped loudly for air and made snorting and choking sounds for at least 10 minutes before going still and dying 24 minutes later, according to witnesses. McGuire, a convicted killer and rapist, felt no pain, Ohio officials officially determined.

Lawyers in the Oklahoma lawsuit allege "a real and immediate threat that the defendants will attempt to execute the plaintiffs using the same drugs and procedures used in the attempted execution of Clayton Lockett, or with similarly untried, untested and unsound drugs and procedures," said the Guardian.

"According to the lawsuit, other problems occurred during the state killings of Robyn L Parks, who gasped and gagged, Scott D Carpenter, who gasped, shook and made a guttural sound, Loyd W LaFevers, who raised up his head and gasped, and Michael L Wilson, who said he felt his body burning."